The present invention relates to image processing systems with an on-screen display function and, more particularly, to a method of storing data of a row buffer into an screen display for minimizing the capacity of a memory by storing both color data and character data into the row buffer and a control circuit thereof.
In methods for displaying characters, there are two types; one uses video RAM (Random Access Memories), and the other uses row buffers.
First, the method using the video RAM comprises the steps of storing both character data and 3-bit color data for displaying the characters into the video RAM, reading the color data stored into the video RAM, and generating the characters with the read color data from a ROM (Read Only Memory).
In other words, the color data stored into the video RAM are read according to input address data, and the characters provided from the ROM have the color data selected in the video RAM, which are applied to a CRT (Cathode Ray Tube) and displayed on a screen.
Second, the method of using the row buffer comprises the steps of storing character data displayed on the screen into a row buffer, and storing the color data of the characters displayed on the screen into another row buffer.
That is, the characters are displayed on the screen by a pair of row buffers.
In both methods, however, if the information of the character data and color data is abundant, the capacity of the video RAM or the row buffer becomes larger. And, a displaying system for processing the character data and the color data is more expanded. Also, if displaying the character data or the color data is not synchronized with a vertical synchronous signal and the processing period of the displaying system exceeds the next display starting time, the fricker phenomenon appears on the screen.